In downhole oil and gas operations downhole equipment, such as downhole valves, sleeves, ICDs, packers, slips, toe sleeves and the like may be operated by use of pressure. For example, some equipment may be operated by use of hydrostatic pressure within the wellbore. In some cases equipment may be actuated by use of pressure differentials, for example between internal tubing pressure and external annulus pressures.
In some known downhole equipment, actuation requires direct use or exposure to downhole fluids, such as annulus fluids. This therefore involves the risk of contamination of the equipment due to particulate matter and the like. This may compromise proper functionality of the equipment, possibly leading to the requirement for workover or intervention operations, which are costly.
It is often the case in downhole operations that a defined sequence of events is required. However, if each event is pressure initiated, then there is a risk of the sequence being upset by a premature reaction of one event or device to a pressure meant for operation of a different event or device. For example, pressure testing is often required in downhole operations, such as to confirm the pressure integrity of completion strings following and/or during deployment. However, should the completion include one or more pressure activated devices then there is a risk that such devices are inadvertently actuated during pressure testing.
Some solutions which seek to ensure correct operational sequencing are known in the art. Some known systems may rely on devices being locked in an initial position, wherein the lock becomes released following a set sequence of events in the well, for example a set sequence of pressures. However, in many cases the lock may be designed to be released upon application of very high elevated pressures, which may even exceed those pressures required for other operations, such as test operations. Such high pressures could lead to compromise of otherwise sound seals and the like.
Electronic solutions are known, which include pressure sensors and controllers which only permit actuation, for example by releasing an initial lock mechanism, following a necessary pressure sequence, such as a pressure test sequence. However, such electronic solutions in some cases may be relatively complex, often requiring the use of sensitive electronics which may be prone to failure in the harsh downhole environment. Further, electronic solutions require a power source, adding to the complexity.
Other solutions may include mechanical arrangements which facilitate operation of downhole devices following a sequence of pressures. Some examples are disclosed in U.S. Pat. Nos. 7,516,792, 6,354,374, 6,230,807 and 7,264,059.
It is also known in the art to include burst disk arrangements, which can initially hold pressure up to their pressure rating, and ultimately fail when the pressure rating is exceeded. This can allow pressures below the rating of the burst disk to be utilized for other operations. However, this solution again requires the burst pressure to be exceeded, meaning that there is no capability of using pressures above the pressure rating of the burst disk, without also causing this to rupture. Further, burst disks can lead to an immediate pressure/force impulse upon rupture, which could cause damage to actuated equipment. Also, conventional burst disks may introduce debris into the downhole equipment.